In a two-cycle engine, generally speaking, the exhaust port and scavenging port, which are formed in the wall of a cylinder, are opened and closed by the operations of a piston so that the exhaust timing is determined in accordance with the opened position of the exhaust port.
More specifically, as the exhaust port comes the closer to a combustion chamber, the exhaust timing is so advanced as to be more appropriate to the high speed running of the engine so that the engine's characteristics are those of the high speed type, in which a high output performance is attained in the high speed run range.
On the contrary, if the exhaust timing is retarded, the engine's characteristics are changed into those of a low speed type.
Thus, according to the current practice, the exhaust timing is determined as to be appropriate to the intermediate speed run range, thereby to provide an engine of the intermediate speed type.